ESSENTIAL KIT - Radar and AISRadar

ESSENTIAL KIT - Radar and AISRadar

Many sea areas of the Med, and indeed around the world, are lonely and peaceful.  When on passage there you can count the number of vessels you encounter on one hand.  However there are other areas where it feels a bit like the M25 in rush-hour.

When it's busy, or in low visibility it's nice to have some electronic eyes watching as well

Radar is the classic addition.  Many different manufacturers, features and ranges are available. For crew safety, mount the antenna high above head height but not too high that yacht heel may affect its ability to scan accurately, around the first spreaders is about right.  Some radar units also incorporate charting features and having a repeater at the helm makes both features much more usable when short or single handed.

With practice they are easy to use but, a bit like chess, there is always more to learn.  If buying new, ensure your unit has MARPA, which will allow you to track other vessels’ speed, course and closest point of approach (CPA).  Its worth saying again - RADAR operation takes practice!

Radar does use a lot of power so monitor your battery levels carefully.   This can be especially troublesome at night when your Solar Panels are not contributing.   As part of upgrading to Radar you should also revisit your battery capacity and charging capabilities to make sure using it won't run you dry on a long foggy night.

Pleasure vessels are not required to have Radar BUT if you do have it you are required to use it whenever low visibility affects a normal lookout   (MCA Col. Regs. Rule 7.)

Remember that different collision regulations apply when operating in low visibility with Radar.  MCA Col Regs Rules 11 thru 18 are the most widely remembered ones relating to collision avoidance but they only apply to vessels "in sight of one another" (Rule 11).  In low viz Rule 19 applies.

The Radar display needs to be visible from the helm especially when sailing short or single handed.  I have a twin display Raymarine system with a 48nm range.  One at the Nav Station and the other at the Helm.  When cruising, I use the 12nm range the most.  I find I get reliable contacts with vessels still invisible to the naked eye and have around 30-40 minutes to decide what action to take.  My MARPA will track up to 10 targets but the small screen rapidly becomes overloaded. Also it relies heavily on your own course & speed remaining constant to calculate the Closest Point of Approach (CPA).  Unfortunately a yacht’s natural movements can confuse the results so a little practice (actually quite a lot of practice) is necessary to interpret the constantly changing CPA value.

The main drawback is that although you can see him and hopefully he can see you, neither knows the other vessel's name so you can't easily call each other.  You will often hear the call “vessel in approx position blah…. heading blah… speed blah…”.   Recognising that they mean you can be quite a stretch.

When the vessel finally comes into sight it can be difficult to relate the real world to the screen especially if more than one vessel is about.   Many Chart Plotter Radar units and PC based chart programs offer a radar overlay onto the chart so it becomes much easier to tie the screen and real world together.


AISRadar isn't actually a radar at all.  It works by VHF radio and relies on vessels transmitting specific details about themselves and their course. Your unit picks up these transmissions and passes this data on either to a chart plotter or PC charting program.

AIS Radar plot1.jpg

The transmitting vessel is displayed in its actual position on the chart with a text box giving its name, call sign, course & speed.  If overlaid onto a radar you will get the CPA too.   Some charting programs also calculate CPA based on their own tracking data.

Green icon vessels are considered to be non-threatening while Red ones will pass within your preset protection range and may need action.


The AIS unit often requires a separate VHF antenna but uses very little power.

Transponder units are now available for pleasure yachts so you can transmit your own details and fully join the fun.   Sadly I do not believe this is always a good thing, you only need to look at the Solent on a sunny weekend to see that too much of a good thing is actually very bad indeed.  

AIS Data Box.jpg

The real advantage of AISRadar is knowledge of the other vessel’s name so you can call them up and agree how you will pass each other if there is any doubt.   The display puts a "box" around the data target.  Some systems will display several data boxes on screen.

The big downside of AIS Radar is that not all ships have them so take care not to focus exclusively on your AIS display. 

Those vessels that do transmit often either don't switch it on or don't update its status so you will see many fast moving vessels claiming to be at anchor.  

AIS Radar is, of course, the pirates dream.  Take care in the less salubrious parts of the world or you might attract some uninvited guests.

Its worth saying again :   AISRadar doesn't show you every vessel in the vicinity, only the ones actively transmitting.

NICE2HAVE KIT - Night Vision Monocular

NICE2HAVE KIT - Night Vision Monocular

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